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  #16  
Old 03-31-2018, 06:05 PM
palincss palincss is offline
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Originally Posted by echappist View Post
No. Unless if the TT is held on gravel roads

Its width leads to nontrivial aero penalty, and its rolling resistance isnt great compared to the truly fast tires
I think once you factor in the wind resistance of the rider, any additional wind resistance due to the difference in width will be trivial, in the noise range.
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  #17  
Old 03-31-2018, 06:23 PM
andrewsuzuki andrewsuzuki is offline
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Y'all are saying low rolling resistance ... it's quite a bit higher than I thought it'd be. At similar tire drop, the GP 4000s II 25mm is ~13w at typical 80psi, while the Bon Jon is ~21w at typical 45psi. That's a huge 16 watt total difference.

First, why? Tread thickness is identical. As for sidewall thickness, the GP is .55mm; the Bon Jon is .6mm. Pretty close. There are faster tires than the GP like the Pro One tubeless that have an even thicker sidewall @ .9mm. What's holding Compass back? Rubber compound?

The main question of course is whether the difference in suspension losses on average pavement is enough to negate the hysteretic loss. There's no question the Bon Jons would be faster on gravel due to ability to run a lower pressure, but at what road quality do road racing tires overtake?

Last edited by andrewsuzuki; 03-31-2018 at 06:32 PM.
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  #18  
Old 03-31-2018, 06:30 PM
andrewsuzuki andrewsuzuki is offline
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Originally Posted by palincss View Post
I think once you factor in the wind resistance of the rider, any additional wind resistance due to the difference in width will be trivial, in the noise range.
Josh Poertner's rule of thumb is +1 aero watt (@30mph) per +2mm width. Tires are kinda complicated because the top half hits the air at twice the velocity of the rider.
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  #19  
Old 03-31-2018, 07:20 PM
Mark McM Mark McM is offline
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Originally Posted by andrewsuzuki View Post
First, why? Tread thickness is identical. As for sidewall thickness, the GP is .55mm; the Bon Jon is .6mm. Pretty close. There are faster tires than the GP like the Pro One tubeless that have an even thicker sidewall @ .9mm. What's holding Compass back? Rubber compound?
Yes, it may very well be the tread compound. The predecessor to the GP4000s was the GP4000, which was dimensionally the same, but used a silica based tread compound. The GP4000 was a bit of a dog when it came to rolling resistance. When Continental replaced the tread compound with a new compound based on nano-sized carbon particles (which they called Black Chili), it had a dramatic reduction in rolling resistance, even lower than other tires with thinner treads made of traditional rubber.

The current lowest rolling resistance tires now all use nano particle carbon compounds, and include tires from Continental (Black Chili compound), Vittoria (Graphene+ compound) and Specialized (Gripton compound -developed by the same engineers that developed Continental's Black Chili).
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  #20  
Old 03-31-2018, 07:27 PM
Mark McM Mark McM is offline
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Originally Posted by andrewsuzuki View Post
Josh Poertner's rule of thumb is +1 aero watt (@30mph) per +2mm width. Tires are kinda complicated because the top half hits the air at twice the velocity of the rider.
Where did you see that? I've heard a different rule from Poertner, the 105% rule. That states that the rim width should be no less than 105% of the tire width for best aerodynamics. Poertner discusses the 105% rule here.

Based on this rule, the absolute tire width is not the predominant factor, matching the tire to the rim is. For example, a 23mm tire on a 24mm rim will actually be faster than 21mm tire on a 20mm rim.
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  #21  
Old 03-31-2018, 07:37 PM
dem dem is offline
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I do wonder if it is related to the huge touring tube used in the test. They definitely felt pretty fast tubeless. Maybe tubes in larger tires cause more rolling resistance than in smaller tires? I have no idea.

(Although I won't use them again due to the bead blowing off at 65 PSI, the leaking weeping sidewalls, and the center pattern was worn off in less than 1000 miles in the rear.)
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  #22  
Old 03-31-2018, 08:41 PM
andrewsuzuki andrewsuzuki is offline
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Originally Posted by Mark McM View Post
Where did you see that? I've heard a different rule from Poertner, the 105% rule. That states that the rim width should be no less than 105% of the tire width for best aerodynamics. Poertner discusses the 105% rule here.

Based on this rule, the absolute tire width is not the predominant factor, matching the tire to the rim is. For example, a 23mm tire on a 24mm rim will actually be faster than 21mm tire on a 20mm rim.
It's actually on the same article you linked

Quote:
In strict aerodynamic terms, this added width comes at a cost of roughly 1watt per 2mm of tire at low yaw angles. However, the big penalty can come at moderate yaw angles as the tires approach the width of the rim.
I think of it like if you have a 17mm rim and the tire's already far beyond 95% of the rim width, what happens if you increase the tire by 2mm.
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  #23  
Old 03-31-2018, 08:56 PM
andrewsuzuki andrewsuzuki is offline
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Originally Posted by Mark McM View Post
Yes, it may very well be the tread compound. The predecessor to the GP4000s was the GP4000, which was dimensionally the same, but used a silica based tread compound. The GP4000 was a bit of a dog when it came to rolling resistance. When Continental replaced the tread compound with a new compound based on nano-sized carbon particles (which they called Black Chili), it had a dramatic reduction in rolling resistance, even lower than other tires with thinner treads made of traditional rubber.

The current lowest rolling resistance tires now all use nano particle carbon compounds, and include tires from Continental (Black Chili compound), Vittoria (Graphene+ compound) and Specialized (Gripton compound -developed by the same engineers that developed Continental's Black Chili).
Interesting. I think I'm going to return these Babyshoe Passes that just arrived and get the G-One Speed Microskin instead. Compass volume + Pro One rubber seems like a good combination.

And now I'm thinking about the Panaracer Gravelking again. It has the "ZSG Natural Compound". Panaracer says "This compound has the same low rolling resistance as the premium compound". Wonder how it compares to the bigger brands.
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  #24  
Old 03-31-2018, 09:10 PM
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fa63 fa63 is offline
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I recently started riding on GravelKing 32mm; they seem to roll really well at 60 psi. I have not noticed any loss of speed on my typical rides.

Quote:
Originally Posted by andrewsuzuki View Post
Interesting. I think I'm going to return these Babyshoe Passes that just arrived and get the G-One Speed Microskin instead. Compass volume + Pro One rubber seems like a good combination.

And now I'm thinking about the Panaracer Gravelking again. It has the "ZSG Natural Compound". Panaracer says "This compound has the same low rolling resistance as the premium compound". Wonder how it compares to the bigger brands.
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  #25  
Old 03-31-2018, 10:52 PM
Jan Heine Jan Heine is offline
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The tests of the Compass Bon Jon Pass tires on www.bicyclerollingresistance.com don’t come as a total surprise, because we knew all along that these drum tests doesn’t replicate the real world. In fact, drum testing was behind the now-discredited belief that narrow tires, run at ultra-high pressures, were faster than wider ones. Today even professional racers ride 25 mm tires at less than 100 psi - on smooth roads – and wider ones on rougher surfaces. If they believed the drum tests, they’d still be on 23 mm rubber inflated to 130 psi or more.

What is a little surprising is that the same tires (Bon Jon Pass with Standard casing) were tested by the respected German magazine TOUR as the fourth-fastest tire in the world. How can we reconcile these dramatically different results?

Drum tests as used by www.bicyclerollingresistance.com suffer from an inherent problem: The convex drum surface digs into the tire. The more supple the tire, the more the drum digs into the tire. The tire is forced to flex more, which absorbs energy. That is why a stiff tire, like the Marathon, performs well on the drum (but not on real roads, which are flat rather than convex).

Increasing the tire pressure makes the tire harder, and so the drum will dig into the tire less. According to the recent drum test, inflating the Bon Jon Pass to 90 psi makes it almost twice as fast compared to 30 psi. They tested the narrower tires at 120 psi, so it’s not surprising that they scored better than the wider tires at 90 psi. Overinflating the Bon Jon Pass to 120 psi would have made it much faster – in their test.

On real roads, higher pressures don’t make tires faster, because the greater hysteretic losses (the tire deforms more) are countered by the lower suspension losses (the bike vibrates less). This is now widely accepted – it’s been shown in test after test, not just by Bicycle Quarterly, but also by Joshua Poertner and others.

The German tests by TOUR magazine didn’t use a drum, but a pendulum on a flat surface – imagine a rocking chair with the runners replaced by bicycle wheels. This eliminates the convex roller digging into the tire. They still don’t have a way to model the rider in their setup, so they don’t measure suspension losses. Even though the Bon Jon Pass scored well in TOUR’s test, I don’t think this totally reflects how it rolls in the real world. It gives an indication how much energy the casing absorbs – which is an important factor, but only half of the equation. On real roads, wider tires will roll faster than TOUR’s test suggests, as they transmit fewer vibrations.

The current ‘Wide Tire Revolution’ came out of real-road testing, with a rider on board. These tests showed that higher pressures don’t make tires faster and that supple, wide tires (which must run at lower pressures) don’t give up any speed to narrow, high-pressure tires. It’s no surprise that our tires, which were designed based on this real-road testing, don’t score well in a drum test.

What we care about is how well our tires roll on real roads, not how well they score in a test that doesn’t replicate the real world. We are excited that many races, on gravel and on paved roads, have been won on Compass tires. We think these results, as well as the real-road testing, give a better indication of their performance.

Jan Heine

Founder

Compass Cycles
www.compasscycle.com
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  #26  
Old 04-01-2018, 12:22 AM
andrewsuzuki andrewsuzuki is offline
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Quote:
Originally Posted by Jan Heine View Post
On real roads, higher pressures don’t make tires faster, because the greater hysteretic losses (the tire deforms more) are countered by the lower suspension losses (the bike vibrates less). This is now widely accepted – it’s been shown in test after test, not just by Bicycle Quarterly, but also by Joshua Poertner and others.
According to Anhalt and Poertner, roller tests correlate very strongly with real-world tests, up until the breakpoint where suspension losses overcome. That breakpoint is actually really pretty high -- ~110psi for the 25mm GP 4000s II and Vittoria Open Corsa. Even for "course intermediate asphalt", it is still quite high at 100psi (which is even above 15% drop = ~88psi according to your chart).

https://silca.cc/blogs/journal/part-...-and-impedance

http://www.slowtwitch.com/Tech/What_...ube__1034.html

Have you commented on Tom's breakpoint theory yet?

---

Also, the 25mm GP 4000S II has a near-identical sidewall and tread thickness to the Bon Jon Pass, yet for the same 15% tire drop (100lb load: ~88psi for GP and ~50psi for Bon Jon) it seems the GP is ahead by a huge ~7-8 watts. Is this to say Compass tires could be much faster from a more advanced rubber compound (as discussed a few posts above)? Similarly, what would you expect if bicyclerollingresistance tested the Cayuse Pass?

Last edited by andrewsuzuki; 04-01-2018 at 12:25 AM.
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  #27  
Old 04-01-2018, 02:11 AM
Jan Heine Jan Heine is offline
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Quote:
Originally Posted by andrewsuzuki View Post
Have you commented on Tom's breakpoint theory yet?
Tom is a great guy, but he tests on even smaller rollers - the ones used for training, so the effect of the convex roller is huge. That is why he finds higher pressures working better.

On real roads, the suspension losses always are considerable. We've tested four different tires at pressures up to 180 psi – on very smooth asphalt – and even in this best-case scenario, there is no linear relationship between pressure and performance... These are real-road tests under very carefully controlled conditions, with excellent repeatability (we test each setup three times) and a rigorous statistical analysis to make sure we are seeing real results and not noise in the data.

Quote:
Originally Posted by andrewsuzuki View Post
it seems the GP is ahead by a huge ~7-8 watts. Is this to say Compass tires could be much faster from a more advanced rubber compound (as discussed a few posts above)?
In TOUR's test, the Bon Jon Pass was ahead of the Conti - it makes you wonder about these drum tests. If anything, TOUR has a bunch of engineers on their testing staff, so within the constraints of their testing (no suspension losses), I'd put more faith in their testing than in most others.

As to the rubber compound, Panaracer's best rubber – which we use for the Compass tires – is actually quite advanced. Panaracer is an engineering-driven company, and they don't care about marketing, so they haven't given their rubber a catchy name.

Jan Heine
Founder
Compass Cycles
www.compasscycle.com

Last edited by Jan Heine; 04-01-2018 at 02:19 AM.
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  #28  
Old 04-01-2018, 02:29 AM
rain dogs rain dogs is offline
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Quote:
Originally Posted by Jan Heine View Post
...

What we care about is how well our tires roll on real roads, not how well they score in a test that doesn’t replicate the real world.

Jan Heine

Founder

Compass Cycles
www.compasscycle.com
The drum test is only one method of test certainly, but all the results are not so in conflict with 'the real world' as you state. I think we need to understand the limits of each test and interpret the results accordingly. Infact, those tires score quite well in rolling resistance even on the drum test.

However, the 'real' world includes other factors commented on by bicyclerollingresistance.com and many others. Can you comment on the findings of:

- punture resistance (which is the harshest criticism in the review I read)
- durability (if i'm doing a 2000km, or 3000km, or 4000km loaded tour how many tires am I going to have to bring?)
- tubeless performance (is the bead holding well on those tires?)

I feel like we're stressing about 1 or 2 watts here or there because of the conditions of the test, and not focusing on all the qualities that make a tire experience. Like punctures and changing a tire on a loaded bickpacking bike on the side of the road. Focusing on those 1 or 2 watts (from a drum test) seems like the least 'real world' thing we could do.
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  #29  
Old 04-01-2018, 06:08 AM
ripvanrando ripvanrando is offline
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Quote:
What we care about is how well our tires roll on real roads
Anyone foolish enough to run Bon Jons at 90 psi better have their life insurance up to date.

They rupture rather spectacularly at 60-70 psi with tubes.
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  #30  
Old 04-01-2018, 08:35 AM
endosch2 endosch2 is offline
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Jan, I would be curious why you don't state your case on slowtwitch. That seems to be the place where all of the engineers discuss this topic and there seems to be a high level of expertise. I think you would provide a valuable contribution there with all of your data.

I know that the tri people are usually concerned with the combination of aero and crr data but they all do the crazy math to combine both.

I don't see why people on this forum would overly obsess about crr data when aero resistance is not a concern for the brevet crowd.

Also can you provide me a link (I have not been around this forum in a while) for where you have done the statistical real world study on why drum testing is so bad?

Last edited by endosch2; 04-01-2018 at 08:39 AM.
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